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SAT® Subject Test in Physics

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Red-Shifted Galaxies

SATPHY-XJ4KFJ

Distant galaxies are seen by astronomers to be red-shifted.

What wave principle explains this, and what does this observation mean about the universe?

A

diffraction; the universe is very old

B

refraction; the universe is expanding

C

polarization; the universe is infinite

D

Doppler effect; the universe is expanding

E

diffraction; the universe is expanding